How to Use PHP array_keys() – Examples & Best Practices

1. What is array_keys()?

• Extracts keys from an array.

• Returns a new indexed array containing the keys.

2. Syntax

php

array_keys(array $array, mixed $search_value = null, bool $strict = false): array  

3. Parameters

• $array → Input array.

• $search_value (optional) → Only return keys matching this value.

• $strict (optional) → Use strict comparison (===).

4. Return Value

• An array of keys.

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5. Practical Examples

Example 1: Basic Key Extraction

php

$user = ['name' => 'Alice', 'age' => 25, 'role' => 'Admin'];  
$keys = array_keys($user);  
print_r($keys);  

Output:

Array ( [0] => name [1] => age [2] => role )  

Example 2: Filter Keys by Value

php

$colors = ['red' => '#FF0000', 'green' => '#00FF00', 'blue' => '#0000FF'];  
$keys = array_keys($colors, '#00FF00');  
print_r($keys);  

Output:

Array ( [0] => green )  

Example 3: Strict Comparison

php

$data = ['a' => '1', 'b' => 1, 'c' => true];  
$keys = array_keys($data, 1, true); // Strict check (type-sensitive)  
print_r($keys);  

Output:

Array ( [0] => b ) // '1' (string) and true are excluded  

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6. Use Cases

• Dynamic Forms: Get field names from config arrays.

• Data Validation: Check if required keys exist.

• API Responses: Extract headers or parameters.

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7. Performance Note

• Works in O(n) time (scales linearly with array size).

• Avoid nested loops with large arrays.

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8. Edge Cases

• Returns empty array if input isn’t an array.

• null values are treated like any other value.

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9. Alternatives

• array_key_exists() → Check if a key exists.

• array_values() → Extract values instead of keys.